Electrical Energy Systems and Power Quality
Core concepts
Understand the power triangle: real power (kW), reactive power (kVAR), and apparent power (kVA), with power factor (PF) = kW/kVA. Utilities often bill for poor power factor or for kVA demand. Know how capacitor banks correct displacement power factor and why harmonic distortion can complicate correction. Candidates should understand demand charges, ratchets, time-of-use rates, and load factor, plus the basics of transformers, conductors, and voltage drop.
Power quality concepts
Know the common disturbances: sags and swells, transients, harmonics (with total harmonic distortion, THD), flicker, and unbalance. Understand that nonlinear loads such as variable frequency drives and electronic ballasts inject harmonics, which can overheat neutral conductors and transformers. Grounding and bonding are foundational. Know that harmonic filters and K-rated transformers address harmonic issues.
Traps to watch
A common trap is assuming capacitors always improve power factor - in harmonic-rich environments they can resonate. Another is confusing demand (kW) with consumption (kWh) when evaluating a demand-reduction measure. Watch for questions that treat leading and lagging power factor as interchangeable; most industrial loads are lagging. Also beware of assuming a ratchet applies only to the current month.
Worked example
A facility draws 800 kW at 0.80 PF, so kVA = 800/0.80 = 1,000 kVA. To reach 0.95 PF, the target kVA is 800/0.95 ≈ 842 kVA. Required capacitor kVAR = √(1,000² − 800²) − √(842² − 800²) ≈ 600 − 262 ≈ 338 kVAR. Verify harmonics before installing.
Practical guidance
Measure with a power quality analyzer over a representative period, log interval data, and correlate disturbances with equipment failures.